1. Field of the Invention
The invention relates to a substrate for mounting an electronic part or electronic parts thereon, the substrate having a laminate structure of an insulation layer and a patterned wiring line layer on each side of a core substrate, and a method of producing the mounting substrate.
2. Description of the Related Art
As an electronic part-mounting substrate having a high density of patterned wiring lines, a substrate having patterned wiring lines formed at both sides of a core substrate, such as a glass-epoxy substrate, made by a build-up process, is known. On such an electronic part-mounting substrate, electronic parts, such as resistors and capacitors, semiconductor elements, and semiconductor devices having a packaged semiconductor element, may be mounted.
FIG. 7 illustrates an example of a printed-circuit board 5 on which electronic parts 6 are mounted. Lead pins 6a are inserted in holes 7 which are formed in the printed-circuit board 5 and have conductor layers 8 formed on their inside walls. The conductor layer 8 extends over the surface of the board 5 to thereby form a land 10. The lead pin 6a is bonded to the conductor layer 8 and the land 10 by solder 9. The formation of the conductor layer 8 and the land 10 is performed by a plating process. The board 5 may have patterned wiring lines on a surface or surfaces thereof, although such wiring lines are not shown in the drawing.
FIG. 8 illustrates an example of prior substrate 4 having two layers of patterned wiring lines 24 (or 24xe2x80x2) formed at each of two sides of a core substrate 20, so as to be formed on an insulation layer 22 (or 22xe2x80x2), which isolate an underlying layer of wiring line and an overlaying layer of wiring line, by a build-up process, and having electronic parts 6 mounted thereon. The patterned wiring lines 24 at one side of the substrate 4 are electrically connected to the patterned wiring lines 24xe2x80x2 at another side by through holes having a structure made up of a hole 26 piercing through the core substrate 20 and a conductor layer 28 formed on the inside wall of the hole 26. Holes 7 in which lead pins 6a are to be inserted are formed so as to pierce through the core substrate 20 as well as the insulation layers 22, 22xe2x80x2, and have conductor layers 8 formed on the inside walls thereof. The lead pins 6a inserted in the holes 7 are bonded to the conductor layer 8 and lands 10, 10xe2x80x2, which are formed around the opening of the holes 7, by solders 9.
FIGS. 9A to 9C show the manufacture of the mounting substrate 4 illustrated in FIG. 8. Referring to FIG. 9A, patterned wiring lines 24 are formed on both sides of a core substrate 20, so as to be formed on an insulation layer 22, 22xe2x80x2, by a conventional build-up process. The patterned wiring lines 24 at one side of the substrate 4 are connected to the patterned wiring lines 24xe2x80x2 at another side by a conductor layer 28 formed on the inside wall of a hole 26 piercing through the core substrate 20. The hole 26 is filled with a resin material prior to the formation of the insulation layers 22, 22xe2x80x2 located directly on the surfaces of the core substrate 20, or is filed with a resin material of a film to be laminated to the core substrate 20 for the formation of the insulation layer 22, 22xe2x80x2 located directly on the surfaces of the core substrate 20.
The core substrate 20 provided with the insulation layers 22, 22xe2x80x2 and the patterned wiring lines 24, 24xe2x80x2 is then drilled to have holes 7 piercing through the core substrate 20 and the insulation layers 22, 22xe2x80x2 at both sides of the core substrate 20, in which holes lead pins 6a of electronic parts 6 (FIG. 8) are subsequently inserted, as illustrated in FIG. 9B.
After the formation of the holes 7, the core substrate 20 is subjected to successive electroless plating and electroplating with copper to have conductor layers 8 on the inside walls of the holes 7 and lands 10, 10xe2x80x2 on the surfaces of the outermost insulation layers 22, 22xe2x80x2. The lands 10, 10xe2x80x2 are formed by patterning conductor layers plated on the outermost insulation layers 22, 22xe2x80x2 by an etching process. Concurrently with the formation of the lands 10, 10xe2x80x2, patterned wiring lines may be formed from the conductor layers on the outermost insulation layers 22, 22xe2x80x2.
In the substrate 4 for mounting electronic parts described above, a material, such as a polyimide or epoxy resin, is used for the insulation layers 22, 22xe2x80x2, and a material, such as a glass-epoxy composite material, is used for the core substrate 20. As a consequence of the difference in materials used for the core substrate and the insulation layers, there is a problem that highly precise formation of holes 7, in which lead pins of electronic parts are to be inserted, by drilling or the like, is difficult. Since in a recent circuit board, miniaturized semiconductor elements and parts are arranged at high density, high precision is needed for the arrangement and sizing of the holes for the insertion of the lead pins, and high precision in making the holes for the insertion of the lead pins is required.
When the plated conductor layer 8 is formed on the inside wall of the hole 7 piercing through the core substrate 20 and the insulation layers 22, 22xe2x80x2, as shown in FIG. 9C, the plated layer 8 has a large thickness to a certain extent. Under the circumstances, the formation of a very small pattern of wiring lines is difficult when the wiring lines are formed, concurrently with the formation of the conductor layer 8 on the inside wall of the hole 7, by patterning the plated conductor layers on the surfaces of the outermost insulation layers 22, 22xe2x80x2 by etching. Although it is possible to form patterns of wiring lines in a high density on the surfaces of the insulation layers 22, 22xe2x80x2 by such a process in which the outer surfaces of the insulation layers 22, 22xe2x80x2 are masked during the plating of the inside walls of the holes 7 for the insertion of lead pins, and the holes 7 are then filled with a resist or the like during the formation of conductor layers for the patterned wiring lines on the surfaces of the insulation layers 22, 22xe2x80x2 by plating, or a process in which the insulation layers on the surfaces of the outermost insulation layers 22, 22xe2x80x2, which have been formed during the plating of the insides of the holes 7, are removed by grinding, and fresh insulation layers for the formation of patterned wiring lines are then formed on the surfaces of the insulation layers 22, 22xe2x80x2, these processes are complicated.
It is an object of the invention to solve the above problems by providing a substrate for mounting electronic parts, which enables electronic parts, such as resistors and capacitors, to be mounted thereon by inserting their lead pins in holes of the substrate, and in which the holes for the insertion of the lead pins can be formed with high precision, and patterned wiring lines can be formed at high density.
It is also an object of the invention to provide a method appropriate for the production of the substrate for mounting electronic parts of the invention.
The substrate for mounting an electronic part or electronic parts thereon according to the invention comprises a core substrate and at least a set of an insulation layer and a patterned wiring line layer, which is formed on the insulation layer, at at least one side of the core substrate, the core substrate having holes, in each of which a lead pin of the electronic part to be mounted is to be inserted, and being provided with lands which surround the opening of the hole and to which the lead pin inserted in the hole is to be bonded, wherein the insulation layer or layers at at least one side of the core substrate has bores, which expose the land at their bottoms, and communicate with the hole.
In an embodiment of the invention, the hole, in which the lead pin of the electronic part is to be inserted, has an inside wall on which a conductor layer is formed. The conductor layer is led to the land to which the lead pin is bonded. The core substrate may have lands which surround the opening of the hole at the side of the core substrate opposed to the side on which the electronic parts are to be mounted, and the conductor layer may be also led to these lands. The land at the side of the core substrate opposed to the side on which the electronic parts are to be mounted can be connected to a wiring line at this side.
The substrate according to the invention may have the holes, in which the lead pin of the electronic part is to be inserted, having an open end at the side of the core substrate opposed to the side on which the electronic parts are to be mounted. The substrate according to the invention may also have the holes, in which the lead pin of the electronic part is to be inserted, having an closed end at the side of the core substrate opposed to the side on which the electronic parts are to be mounted. The end of the hole at the side of the core substrate opposed to the side on which the electronic parts are to be mounted may be closed by the insulation layer on the core substrate, a metal layer provided at the end of the hole, or a metal film formed during the formation of the wiring line layer. In the substrate having the holes with the closed end, a wiring line can be provided on the insulation layer at an area corresponding to the location of the hole with the closed end.
The substrate according to the invention may have a hole piercing through the core substrate and having an inside wall on which an conductor layer is provided to connect a wiring line at one side of the core substrate to another wiring line at the opposed side.
The substrate according to the invention can be manufactured by a method comprising the steps of providing a core substrate, forming holes piercing the core substrate, forming, on the core substrate and around the ends of the holes, lands for the connection with the lead pin of the electronic parts to be mounted, filling the holes with a filling material, such as a resin, forming at least a set of an insulation layer and a patterned wiring line layer, which is formed on the insulation layer, at at least one side of the core substrate, by a build-up process, forming bores piercing through the resultant insulation layer or layers and exposing the land at their bottom, and removing the filling material in the holes to allow each of them to communicate with each of the bores.
The formation of the bores and the removal of the filling material in the holes may be carried out using a laser beam. The formation of the bores and the removal of the filling material in the holes may be also carried out by chemical etching.